Grid-controlled electron discharge device



April 3, 1951 n. e. BURNSIDE 2,547,372 GRID-CONTROLLED ELECTRON DISCHARGE DEVICE Filed Sept. 25, 1945 INVENTOR 12 Dow 650mm? BY @414 W ATTORNEY Patented Apr. 3, 1951 Don G. Burnside, Princeton, N'. J., assignor to Radio Corporation of America, a corporation of Delaware Application seae'mba 25, 1945, seam. 618,468

1'0 Glaims'. (Cl. 250-275) My invention relates to electron discharge devices" and more particularly to such devices utilized as oscillators and employing cavity resonators. r

Triodes designed to operate as oscillators in cavity" resonator type circuits are often constructed in such a manner that the capacitance between anodes andcathodes is unusually'low; This anode-to-cathode' capacitance is'{ ordinarily so'small that it alone will not cause oscillations and in this event some provision must be made to provide directed feedback by circuit design. Several circuit arrangements that will provide the",nece' ssary feedback are possible, but-allof them c'ause substantialcircuit complications and tuning or adjustment difilculties. method that permits the advantage of'circuit simplicity, and in general requires no adjustments for feedback, is that which results from building into the tube additional anode and catho'de'c apaci'tance. When oscillations occur; due to internal anode-to-c'athode capacitance, the feed back is more nearly independent of the operating conditions than with external circuit feedback. It also provides" better phase angle relations be tween grid and anode voltages and there are no adjustments to be made once the proper capacifence is found forjagiven application. 1 I While it is recognized that themo'st efiective placefor feedback capacitance is generally in the anode-cathode space; that is, through the grid itsen; grids which havewidely spaced wires result in relatively large capacitanceb'et'ween anode and cathode, but such grids also harmfully-affect the tube'characteristic and consequently cause poor performance in the circuits considered. I t'is,'therefore', an "object of my invention 6 providean improved type electron discharge de 'vi'ce'util'ized as anoscillatorin' a cavity resonator circuit but'whichrequiresno external feedback; -"Another object or; myinvention is} t c-provide such a device in Whichf'eedback' through'the grid is provided but which nevertheless" avoids-the harmful effects" associated with g rids having widelyspaced wires. 1 i i f'A mor'e specific object of' my invention is to provide an electron discharge device ofthe type described in which the amountof feedback through theg'rid can be controlled-atwill. .The novel features which Ibeli'eve to be characteristic of my invention are set forth with par; .ticularity in the appended claims, but the inventionitself willbest beund'erstocd by referenceto the following des'criptionf taken. in. co'nnection with the accompanying drawingin" which'F'igure 1 is a longitudinal section of an electron discharge device made according to my invention and its associated pavity resonator circuit, Figure 2 is a section taken along the line 22 of Figure 1, Figure 3.is a partial longitudinal section of a modification of the electron discharge device shown in Figure 1, and Figure 4 is'a still further modification of the electron discharge device shown in Figure 1' employing means for controlling the anode-cathode capacitance and hence.

the feedback. 7

In accordance with my invention the grid is provided with a large aperture having a definite boundary, preferably at'the center of' the grid, and is located over a portion of the cathode which is free from emitting material. Under these conditions a portion of the radio frequency voltage developed'on the anode is transferred to the cathode through the aperture in such phase as to maintain oscillations. One such an arrangement is" that shown in Figure 1. h

In this arrangement I provide an inverted cupshaped indirectly heated cathode l coated on its upper surface, except for the portion shown at it)". A heater H is provided for the cathode having leads I l' extending therefrom. The cathode is provided with a support and contact ring l2 on which the cathode IE] is supported by means of the conducting elements ['3 of reduced transverse section for suppressing heat losses from the cathode. A cup-shaped member M of insulating material, preferably glass,'is sealed to the cathode ring. Positioned above'the cathode is an annular grid or grid assembly having an outer gridring l and an inner grid ring I6, to which the equallyspaced parallelgrid wiresl! are secured. This grid is thus provided with an aperture I8 of substantial area which registers with the uncoated surface [6' of the cathode" l0. Sealed between the cathode ring l2 and the grid ringfl which serveas radially'directed supports and leads, is the insulating collar 19 sealed to the rings. Mounted above the grid is the anode 20 which may be a solid cylindrical block preferably of copper and having heat radiators 2| and the inverted cup shaped collar 22 hermetically sealed to theanode and in turn having the insulating 'ber 25' and outer tubular member .26, the inner member supporting a contact collar 21 capaci tively coupled to the inner tubular member 25 through insulating collar 28, the spring fingers 29 contacting the cathode ring l2. The output resonator 30 is provided with the spring fingers 3| which contact the grid ring I and with the collar 32 capacity coupled through insulating collar 33 to the collar 34. The spring contact fingers 35 may be carried by collar 34 or anode ring 24 as shown. Energy may be extracted from resonator 30 by any suitable means, such as a coupling loop 36 forming a continuation of the inner conductor of a coaxial line 3'! which is closed by an insulating seal 38.

It will thus be seen that the only coupling between the two resonators is bymeans of the oathode-anode capacity through the aperture 18 and whatever small capacity exists between the other portions of the cathode and anode. The size of the aperture I8 is made such as to provide the desired capacity coupling. While shown in connection with plate-like electrodes, the invention may be applied to cylindrical cathodes and either helical, mesh or squirrel cage type grids.

If it should be undesirable to unduly reduce cathode. and grid areas, but at the same time it is desired to maintain the feedback capacitance, an elevated section of the cathode could be extended upward into the grid aperture which can be made smaller and thus nearer the anode. This extended area, which is uncoated, can thus be smaller than the uncoated area in the first form in Figure l and still provide the same capacity. Such an arrangement is shown in Figure 3 in which the cathode ID is provided with a bosslike extension 50" which extends into the grid aperture it which can be made smaller than in the form shown in Figure 1.

-;A modification of the arrangement shown in Figure 3 is shown in Figure 4. In this case the cathode 49 is provided with aperture M in which is mounted a disc-like element 42 electrically connected to the cathode and supported by the oathode ring I2 by means of the disc 44 and the conducting elements 45. A rod 43 extends between disc .2 and disc 44. The rod could be made adjustable relative to the disc 44 so that the disc can be positioned at any point between the surface of the cathode and the surface of the anode 20. In the arrangements shown supporting elements 45 can be made of thermionic material which expands or contracts so that positioning of the disc could be changed by external means; for example, by causing current to fiow from source 46 through supporting elements 45 and a flexible conductor 43, the amount of current and hence the expansion and contraction of the elements 45 being governed by a rheostat 41. Thus the anode-to-cathode capacitance can be altered by a predetermined amount without making necessary an alteration in aperture size or anode spacing. The capacitance can be changed if desired .by simply building the tube with the disc higher or lower, or by utilizing the arrangement shown in Figure 4.

While I have indicated the preferred embodiments of my invention of which I am now' aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is emplyed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is:

1. An electron discharge device having an evacuated envelope containing a cathode and an oppositely disposed anode, and a grid positioned between said cathode and anode and shielding said cathode from said anode, said grid comprising equallyr-spaced parallel wires, said cathode having an emitting portion and a substantially nonemitting portion, said grid having an aperture registering with said non-emitting portion and through which said cathode and anode are capacitively coupled, said wires adjacent said aperture being supported by a grid ring.

2. An electron discharge device having an evacuated envelope containing a cathode and an oppositely disposed anode, and a grid positioned between said cathode and anode and shielding said cathode from said anode, said grid comprising equally-spaced parallel wires, said cathode having an emitting area and a non-emitting area positioned centrally thereof, said grid having an aperture therein registering with said non-emitting area whereby the cathode-to-anode capacity is increased, said wires adjacent said aperture be ing supported by a grid ring.

3. An electron discharge device having a cupshaped cathode and an oppositely disposed anode, the closed end of said cathode facing said anode, the surface of said cup-shaped cathode being coated with emitting material and having a nonemitting portion at the center thereof, a substantially fiat grid positioned between said cathode and said anode and comprising equally-spaced parallel wires and having an aperture registering with said non-emitting portion of said cathode for increasing the capacity between said cathode and anode through said grid, said wires adjacent said aperture being supported by a rid ring.

4. An electron discharge device according to claim 1, having a cathode of substantial area and having a portion of said cathode surface lying in a different plane from the remainder of said cathode, said grid aperture registering with the portion of said cathode lying in a different plane for increasing the capacity between said cathode and said anode.

5. An electron discharge device according to claim 1, having a cathode of substantial area and having a portion of said cathode surface extended therefrom and lying in a different plane from the remainder of said cathode, said grid aperture receiving the extended portion of said cathode for increasing the capacity between said cathode and said anode.

6. An electron discharge device according to claim 1, having an inverted cup-shaped cathode, said cathode having an aperture in the top-thereof, said grid aperture registering with the aperture in said cathode, and a disc supported by said cathode within said aperture in said cathode for increasing the capacity between-said cathode and anode through said grid. I

'7. An electron discharge device according to claim 1, having an inverted cup-shaped cathode, said cathode having an aperture in the top there of, said grid aperture registering with the aperture in said cathode, and a disc supported by said cathode within said aperture in said oath:

ode for increasing the capacity between said cathode and anode through said grid, and means secured to said cathode for supportingsaid disc and including thermostatic elements for varying the position between said disc and the surface of said anode in response to current through said thermostatic elements. I

8. An electron discharge device according to claim 1, having an inverted cup-shaped cathode having a cathode ring support, said cathode having an aperture in the top thereof, said grid aperture registering with the aperture in said cathode, a disc supported by said cathode within said aperture in said cathode for increasing the capacity between said cathode and anode through said grid, and means secured to said cathode ring support for supporting said disc and including thermostatic ribbon-like elements for varying the position between said disc and the surface of said anode in response to current through said thermostatic elements.

9. An electron discharge device having an evacuated envelope containing an envelope and containing a cathode of substantial area, said cathode having radially directed conducting and supporting means extending through the envelope, an anode oppositely positioned to said cathode and a grid positioned between said cathode and anode and having a radially directed supporting and conducting means extending through said envelope whereby said cathode is shielded from said anode by said grid, said grid comprising equally-spaced parallel wires, said cathode having emitting and non-emitting portions, said grid having an aperture registering with the non-emitting portion of said cathode whereby the anode-to-cathode capacity is increased, said wires adjacent said aperture being supported by a grid ring.

10. An electron discharge device including a cathode, an anode disposed opposite said cathode and an annular grid positioned between and partially shielding said cathode and said anode, said annular grid comprising inner and outer grid rings having equally-spaced parallel wires attached to and bridging the annular space between said grid rings, whereby cathode and anode are capacitively coupled through said inner grid ring.

DON G. BURNSIDE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,091,443 Heintz Aug. 31, 1937 2,134,577 Putzer Oct. 25, 1938 2,316,264 Litton Apr. 13, 1943 2,331,398 Ingram Oct. 12, 1943 2,400,753 Haefi May 21, 1946 2,416,565 Beggs Feb. 25, 1947 

